Few works exist on oxygen implantations in ZnO and none discloses the possibility of p-type doping by means of an oxygen implantation.
Indeed, the documents describing the results obtained after implantation of oxygen in ZnO essentially relate to the characterisation of defects created by the implantation.
Document [1] of Chen et al. describes the implantation of O+ or B+ ions in non doped ZnO having an n-type conductivity. After the implantation, the samples are annealed at a temperature from 200° C. to 1000° C. for a time of 30 minutes under nitrogen. An annealing temperature from 900° C. to 1000° C. is necessary to eliminate the microvoids in the samples implanted by B+ ions, whereas a temperature of 700° C. to 800° C. is sufficient to eliminate the vacancies in the samples implanted by O+ ions.
No electrical characterisation result demonstrating a p-type conductivity is provided in this document.
Document [2] of Chen et al. shows by “positron annihilation” or by “Raman” studies the evolution of vacancy clusters induced by implantation, depending on the recovery annealing temperature, for samples of ZnO implanted with N+, O+, or Al+ ions alone or co-implanted with O+/N+ or Al+/N+ ions. In the samples implanted with N+ ions and the samples co-implanted with Al+/N+ ions, the vacancy clusters are only partially eliminated by annealing at 800° C., whereas they are completely eliminated in the samples implanted with O+ or Al+ ions by annealing at 800° C.-900° C. In the samples co-implanted with O+/N+ ions, most of the vacancy clusters are eliminated at 800° C., during another annealing at 1000° C.-1100° C., the nitrogen also forms stable complexes with the thermally generated vacancies. It is shown in this document that an annealing at 1200° C.-1250° C. makes it possible to eliminate these vacancy complexes formed by the implantation of nitrogen but no electrical characterisation result demonstrating a p-type conductivity is provided.
Document [3] of Zhao et al. discloses photoluminescence characterisation results of samples of ZnO implanted by oxygen and zinc then annealed in oxygen for 10 minutes at 500° C., then for 10 minutes at 700° C., which reveal the existence of a peak which may correspond to the presence of an OZn antisite.
This hypothesis is moreover confirmed in document [4] of Vijayakumar et al. in which is revealed by optical absorption, in samples of ZnO implanted by oxygen ions and without annealing, the presence of levels attributed to Zn vacancies (VZn), OZn antisites and oxygen vacancies (VO).
The Hall effect measurements performed in this document [4] also show a considerable increase in the resistivity of the implanted layers and an increase in the concentration of carriers.
Document [5] describes a method of producing a buried semi-insulating ZnO layer co-implanted by oxygen and nitrogen ions, for “MESFET”.
Oxygen and nitrogen ions are implanted together, simultaneously in equal quantities in a surface layer of zinc oxide and said layer is subjected to a thermal treatment at 800° C.
The square of the resistivity measured by Hall effect of the semi-insulating layer formed by the co-implantation followed by annealing is given at 107Ω/□.
Consequently, in view of the foregoing, there exists a need that has not yet been met for a method of preparing p-type doped zinc oxide ZnO which has effectively a p-type behaviour.
There also exists a need for a method of preparing p-type doped zinc oxide ZnO that is simple and reliable.